Intraluminal medical devices designed for use in treating vascular diseases are often inserted into the vasculature of a patient at a point remote from the treatment site. For instance, an intravascular catheter may be introduced into the femoral artery through an incision in the groin area, and is then advanced through the femoral artery to the coronary treatment site. The vessels through which the catheter travels are small and the passage through the vessel is tortuous making positioning of the catheter difficult, and can be quite often uncomfortable for the patient. It is therefore desirable to make this procedure as atraumatic to the patient as possible. This, consequently, requires the catheter to have specific performance characteristics. These characteristics include lubricity, trackability, pushability, and so forth. However, while the catheter requires a certain amount of flexibility in order to have good maneuverability and trackability through the vessels, it must also be sufficiently strong in the longitudinal direction so as not to buckle or kink when crossing lesions. Also, balloon catheters require that the walls be made of a sufficiently strong material to withstand rupture because they are inflated under extremely high pressure.
In order to achieve a combination of the desired properties, more than one type of material may therefore be employed in the construction of a catheter. The construction may therefore involve bonding or fusing together of various parts through the use of adhesives, or through a welding process, for instance. An example is one in which a dilatation balloon is adhered or fused to a catheter shaft. The balloon and catheter outer shaft materials must therefore be of a bondable nature.
Polymeric materials that are not inherently lubricious are typically more easily bonded. However, this also makes insertion and maneuverability of the catheter more difficult. Therefore, if the polymer is not lubricious in nature, lubricants are often added to the outer surface. Use of lubricants, however, also complicate the bonding process.
Further, the inner surfaces of tubing used in intraluminal devices must also meet certain performance criteria. For instance, the inner surface of a catheter shaft must produce low surface friction when in contact with the guidewire. This low surface friction facilitates advancement of the catheter over the guidewire, for instance. This can also be accomplished, for example, by the use of lubricious coatings, such as polytetrafluoroethylene (PTFE) which has been used as a coating on the inner lumen surface of a catheter shafts.
It is difficult to find one material that meets all of the performance requirements. Therefore, it is often also desirable to manufacture tubing for medical devices that have more than one layer of material. This too involves adhering or fusing together of the layers.
Multilayered tubing has been used to provide medical tubing with the combination of desirable properties. For instance, U.S. Pat. No. 6,165,166 provides a coextruded flexible tubing. The multilayer structure comprises a core layer of a lubricious polymeric material, an outer layer comprising directly bondable polymer, and an intermediate tie layer comprising a polymer having a pendant functionality capable of adhering the lubricious material of the core layer to the directly bondable material of the outer layer. The intermediate tie layer provides a strong connection between the core layer and the outer layer.